Sheet conveying device, image forming apparatus, and method of determining whether multi-feed has occurred

ABSTRACT

A sheet conveying device includes: a sending unit configured to send an ultrasonic wave; a receiving unit positioned to face the sending unit across a conveyance path, along which a sheet is conveyed, and configured to receive a first ultrasonic wave, the first ultrasonic wave being an ultrasonic wave sent from the sending unit and passed through the sheet, and output a first voltage corresponding to the first ultrasonic wave; an adjusting unit configured to adjust the first voltage into an adjusted first voltage according to a setting; an amplification unit configured to amplify the adjusted first voltage by a preset amplification factor for multi-feed determination into an amplified first voltage; and a determining unit configured to determine whether or not multi-feed of the sheet has occurred based on the amplified first voltage.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and incorporates by referencethe entire contents of Japanese Patent Application No. 2014-054213 filedin Japan on Mar. 17, 2014.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet conveying device, an imageforming apparatus, and a method of determining whether multi-feed hasoccurred.

2. Description of the Related Art

Techniques of determining whether or not multi-feed of sheets hasoccurred (hereinafter, “multi-feed determination”) based on differencein amount (e.g., an amount of attenuation) of an ultrasonic wave betweenbefore and after passing through a sheet(s) being conveyed areconventionally known. Meanwhile, the difference in amount of theultrasonic wave largely depends not only on the factor of the sheet butalso on the factor other than the factor of the sheet. Accordingly,devices (devices that make multi-feed determination) undesirably varyfrom each other in the difference in amount of the ultrasonic wave,which leads to a false multi-feed determination.

Examples of the factor of the sheet include basic weight of the sheet.Examples of the factor other than the sheet include variation in timingof sending an ultrasonic wave by a sending sensor, variation in timingof receiving an ultrasonic wave by a receiving sensor, variation inarrangement of the sending sensor and the receiving sensor, anddevice-to-device environmental variation (e.g., variation in thetemperature, the humidity, or the like).

A technique of adjusting an amplification factor of an amplifier circuitof a signal output by a receiving sensor receiving a ultrasonic wave isdisclosed in, for example, Japanese Laid-open Patent Application No.2006-312527. According to the technique disclosed in Japanese Laid-openPatent Application No. 2006-312527, device-to-device variation in thedifference in amount of the ultrasonic wave can be adjusted, andoccurrence of false multi-feed determination can be reduced.

However, such a conventional technique as that described above thatadjusts variation in the difference in amount of the ultrasonic wave byusing an amplification factor of an amplifier circuit is disadvantageousin that noise filtering characteristics of the amplifier circuit arealso undesirably changed, undesirably causing oscillation of anoperational amplifier or the like to occur. As a corollary to this,multi-feed determination will fail. For this reason, such a conventionaltechnique as that described above is susceptible to improvement inaccuracy of multi-feed determination.

In light of the foregoing, there is a need for a sheet conveying device,an image forming apparatus, and a multi-feed determination method withimproved accuracy of multi-feed determination.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve theproblems in the conventional technology.

A sheet conveying device includes: a sending unit configured to send anultrasonic wave; a receiving unit positioned to face the sending unitacross a conveyance path, along which a sheet is conveyed, andconfigured to receive a first ultrasonic wave, the first ultrasonic wavebeing an ultrasonic wave sent from the sending unit and passed throughthe sheet, and output a first voltage corresponding to the firstultrasonic wave; an adjusting unit configured to adjust the firstvoltage into an adjusted first voltage according to a setting; anamplification unit configured to amplify the adjusted first voltage by apreset amplification factor for multi-feed determination into anamplified first voltage; and a determining unit configured to determinewhether or not multi-feed of the sheet has occurred based on theamplified first voltage.

A method determines whether or not multi-feed has occurred. The methodincludes: sending an ultrasonic wave; receiving including receiving theultrasonic wave passed through a sheet conveyed along a conveyance pathand outputting a voltage corresponding to the ultrasonic wave; adjustingthe voltage into an adjusted voltage according to a setting; amplifyingthe adjusted voltage by a preset amplification factor for multi-feeddetermination into an amplified voltage; and determining whether or notmulti-feed of the sheet has occurred based on the amplified voltage.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view schematically illustrating an example of amechanical structure of a sheet conveying device according to anembodiment;

FIG. 2 is a block diagram illustrating an example of an electricalstructure of the sheet conveying device according to the embodiment;

FIG. 3 is a flowchart illustrating an example of an adjustment operationaccording to the embodiment;

FIG. 4 is an explanatory diagram of setting adjustment according to theembodiment;

FIG. 5 is a diagram illustrating an example of a circuit configurationof a receiving sensor and an adjusting unit according to the embodiment;

FIG. 6 is a flowchart illustrating an example of a failure determinationoperation according to the embodiment; and

FIG. 7 is a block diagram illustrating an example of a hardwareconfiguration of an image forming apparatus to which the sheet conveyingdevice according to the embodiment is applied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are described in detailbelow with reference to the accompanying drawings. The sheet conveyingdevice described in each embodiment may be applied to an image formingapparatus such as an MFP (multifunction peripheral), a copier, aprinter, a scanner, or a facsimile. An MFP is an apparatus having atleast two of a copier function, a printer function, a scanner function,and a facsimile function.

FIG. 1 is a side view schematically illustrating an example of amechanical structure of a sheet conveying device 100 according to anembodiment. As illustrated in FIG. 1, the sheet conveying device 100includes a sheet feeding tray 102, a pickup roller 104, sheet feedingrollers 106 a and 106 b, a conveyance path 108, conveyance rollers 110 aand 110 b, a sending sensor 112 (an example of “sending unit”), and areceiving sensor 114 (an example of “receiving unit). The pickup roller104, the sheet feeding rollers 106 a and 106 b, and the conveyancerollers 110 a and 110 b are driven to rotate by a drive device (notshown).

A stack of a plurality of sheets is housed in the sheet feeding tray102. The pickup roller 104 is in contact with an uppermost sheet P ofthe sheets in the sheet feeding tray 102. The pickup roller 104 rotatescounterclockwise, thereby picking up the sheet P with which the pickuproller 104 is in contact.

The sheet feeding rollers 106 a and 106 b rotate counterclockwise andclockwise, respectively, thereby feeding the sheet P picked up by thepickup roller 104 to the conveyance rollers 110 a and 110 b along theconveyance path 108.

The conveyance rollers 110 a and 110 b rotate clockwise andcounterclockwise, respectively, thereby further conveying the sheet Pfed from the sheet feeding rollers 106 a and 106 b along the conveyancepath 108.

The sending sensor 112 and the receiving sensor 114 are positioned toface each other across the conveyance path 108. The sending sensor 112is a sensor that sends an ultrasonic wave. The receiving sensor 114 is asensor that receives the ultrasonic wave sent from the sending sensor112. If the ultrasonic wave passes through the sheet P, the ultrasonicwave is attenuated by the sheet P and then received by the receivingsensor 114. The thus-received ultrasonic wave is used in variousdeterminations including determination as to whether or not multi-feedhas occurred (hereinafter, “multi-feed determination”) and determinationas to whether or not a failure has occurred (hereinafter, “failuredetermination”).

The sheet P delivered by the conveyance rollers 110 a and 110 b passesthrough a position of the sending sensor 112 and the receiving sensor114. Thereafter, an image is transferred onto the sheet P by an imageforming unit (not shown). Hence, the image is formed (printed) on thesheet P.

FIG. 2 is a block diagram illustrating an example of an electricalstructure of the sheet conveying device 100 according to the embodiment.As illustrated in FIG. 2, the sheet conveying device 100 includes thesending sensor 112, the receiving sensor 114, an adjusting unit 130, anadjustment control unit 140, an amplification unit 150, and adetermining unit 160.

The sending sensor 112 is the sensor that sends an ultrasonic wave.

The receiving sensor 114 is the sensor that receives the ultrasonic wavesent from the sending sensor 112 and converts the received ultrasonicwave into a voltage representing the ultrasonic wave.

The adjusting unit 130 is a circuit that adjusts the voltage, into whichthe ultrasonic wave is converted by the receiving sensor 114, accordingto setting of the adjusting unit 130 adjusted by the adjustment controlunit 140.

The adjustment control unit 140 is a circuit that adjusts the setting ofthe adjusting unit 130 and determines whether or not at least any one ofthe sending sensor 112, the receiving sensor 114, and the adjusting unit130 has failed by utilizing adjustment of the setting.

The amplification unit 150 is a circuit that amplifies the voltageadjusted by the adjusting unit 130 by a preset amplification factor formulti-feed determination (hereinafter, the “presetmulti-feed-determining amplification factor”).

The determining unit 160 is a circuit that determines, based on thevoltage amplified by the amplification unit 150, whether or notmulti-feed of sheets has occurred and whether or not at least one of theadjusting unit 130 and the amplification unit 150 has failed.

Note that elements of the electrical structure of the sheet conveyingdevice 100 are not necessarily limited to those described above. Forexample, a detector circuit may be interposed between the amplificationunit 150 and the determining unit 160.

How the sheet conveying device 100 operates is specifically describedbelow. Hereinafter, it is assumed that there are the followingdevice-to-device (device: the sheet conveying device 100) variations.Relative to a value of an ultrasonic wave sent by the sending sensor112, a value of the ultrasonic wave received by the receiving sensor 114is attenuated by the factor other than the sheet by approximately 15decibels (dB) at maximum in some devices, while the same is amplified byapproximately 15 dB at maximum in some other devices. The same isattenuated by the factor of the sheet in a range from approximately 37dB to approximately 55 dB.

In short, the discussion below is based on the assumption that thedevice-to-device variation in the value of the ultrasonic wave receivedby the receiving sensor 114 caused by the factor other than the factorof the sheet is 30 dB; the same caused by the factor of the sheet is 18dB. However, this is not a restrictive assumption.

An adjustment operation applied to the setting of the adjusting unit 130is described below with reference to FIGS. 3 and 4. FIG. 3 is aflowchart illustrating an example of the adjustment operation accordingto the embodiment. FIG. 4 is an explanatory diagram of an example ofsetting adjustment according to the embodiment.

Meanwhile, the adjustment operation is performed in a state where nosheet is conveyed by the sheet conveying device 100. For example, theadjustment operation may be performed before factory shipment or duringmaintenance of the sending sensor 112, the receiving sensor 114, and/orthe like. In short, the adjustment operation is performed before a userperforms a job, such as a print job, that uses a sheet.

The receiving sensor 114 receives an ultrasonic wave (an example of“second ultrasonic wave”) sent from the sending sensor 112 and reachingthe receiving sensor 114 without passing through a sheet, converts thereceived ultrasonic wave into a voltage (an example of “second voltage”)representing the ultrasonic wave, and outputs the voltage to theadjusting unit 130.

Thereafter, the adjustment control unit 140 determines whether or notthe output value, which is the value of the voltage output from theadjusting unit 130, is equal to or higher than a first reference value(S101). More specifically, the adjusting unit 130 adjusts the voltageaccording to default setting of the adjusting unit 130 and outputs thevalue of the adjusted voltage at S101.

The first reference value is, for example, a voltage value obtained bysubtracting, from the voltage value representing the ultrasonic wavesent from the sending sensor 112, a voltage value corresponding to amaximum amount of attenuation of the ultrasonic wave possibly caused bythe factor other than the factor of the sheet until when the ultrasonicwave is received by the receiving sensor 114.

In the embodiment, it is assumed that the ultrasonic wave is attenuatedby the factor other than the factor of the sheet by 15 dB at maximum.Accordingly, the first reference value can be obtained by subtracting avoltage value corresponding to 15 dB from the voltage value representingthe ultrasonic wave sent from the sending sensor 112.

If the output value of the adjusting unit 130 is lower than the firstreference value (No at S101), the adjustment control unit 140 determinesthat at least any one of the sending sensor 112, the receiving sensor114, and the adjusting unit 130 has failed (S103).

For example, when the output value of the adjusting unit 130 is anoutput value 201 which is lower than the first reference value asillustrated in FIG. 4, the adjustment control unit 140 determines thatat least any one of the sending sensor 112, the receiving sensor 114,and the adjusting unit 130 has failed.

More specifically, the adjustment control unit 140 determines that afailure such as an inactive state of the sending sensor 112, an inactivestate of the receiving sensor 114, a decrease in sensitivity (such assystem sensitivity, impedance, or impulse responsivity) of the receivingsensor 114, or a failure of an adjustment circuit has occurred, andsends a notification of the failure to a control unit (not shown) or thelike so that the failure is displayed on a display unit (not shown) orthe like.

On the other hand, if the output value of the adjusting unit 130 isequal to or higher than the first reference value (Yes at S101), theadjustment control unit 140 determines whether or not the output valueof the adjusting unit 130 is lower than a second reference value (S105).

The second reference value is, for example, a voltage value within arange between the first reference value and a voltage value obtained bysubtracting, from the voltage value representing the ultrasonic wavesent from the sending sensor 112, a voltage value corresponding to aminimum amount of attenuation of the ultrasonic wave possibly caused bythe factor other than the factor of the sheet until when the ultrasonicwave is received by the receiving sensor 114.

In the embodiment, it is assumed that the ultrasonic wave is amplifiedby the factor other than the factor of the sheet by 15 dB at maximum.Accordingly, the second reference value can be obtained as a voltagevalue in a range between the first reference value and a voltage valueobtained by adding the voltage value corresponding to 15 dB to thevoltage value representing the ultrasonic wave sent from the sendingsensor 112. In short, the second reference value is a voltage value in arange of 30 dB from the first reference value. In the example describedabove, a value obtained by adding a voltage value corresponding 1 dB tothe first reference value is used as the second reference value.However, the second reference value is not limited thereto.

If the output value of the adjusting unit 130 is equal to or higher thanthe second reference value (No at S105), the adjustment control unit 140determines whether or not the adjusting unit 130 can decrease thevoltage fed from the receiving sensor 114 or, in other words, whether ornot it is possible to adjust the setting of the adjusting unit 130 so asto decrease the voltage (S107).

Here, the adjustment control unit 140 is capable of causing theadjusting unit 130 to decrease the voltage by adjusting the setting ofthe adjusting unit 130 to setting different from the default setting. Inthe embodiment, the variation of the voltage representing the ultrasonicwave caused by the factor other than the factor of the sheet is within avoltage range corresponding to a 30-dB range. Accordingly, theadjustment control unit 140 can cause the adjusting unit 130 to decreasethe voltage by a value corresponding to 30 dB, which is adjustmentlimit, at maximum. Note that the adjusting unit 30 is structurallycapable of decreasing the voltage by a value corresponding to 30 dB orhigher; the adjustment control unit 130 is structurally capable ofcausing the adjusting unit 130 to decrease the voltage by a valuecorresponding to 30 dB or higher.

If the adjusting unit 130 cannot decrease the voltage fed from thereceiving sensor 114 (No at S107) or, more specifically, the adjustingunit 130 cannot deliver an output value lower than the second referencevalue because the setting of the adjusting unit 130 is at the adjustmentlimit of the adjustment control unit 140 and therefore the adjustingunit 130 cannot decrease the voltage any more, the adjustment controlunit 140 determines that at least any one of the sending sensor 112, thereceiving sensor 114, and the adjusting unit 130 has failed (S109).

For example, when, in a condition where the setting of the adjustingunit 130 does not allow a further decrease in the voltage, the outputvalue of the adjusting unit 130 is an output value 202 which is higherthan the second reference value as illustrated in FIG. 4, the adjustmentcontrol unit 140 determines that at least one of the sending sensor 112,the receiving sensor 114, and the adjusting unit 130 has failed.

More specifically, the adjustment control unit 140 determines that afailure such as an overvoltage in a drive circuit of the sending sensor112, a condition in which the sensitivity (such as the systemsensitivity, the impedance, or the impulse response) of the receivingsensor 114 are high and out of standard, disconnection of a connector ofthe receiving sensor 114, or breakage of a harness of the receivingsensor 114 has occurred, and sends a notification of the failure to thecontrol unit (not shown) or the like so that the failure is displayed onthe display unit (not shown) or the like.

On the other hand, if the adjusting unit 130 can decrease the voltagefed from the receiving sensor 114 (Yes at S107), the adjustment controlunit 140 adjusts the setting of the adjusting unit 130 and causes theadjusting unit 130 to decrease the voltage fed from the receiving sensor114 (S111). Thereafter, processing goes back to S105.

At S105, if the output value of the adjusting unit 130 is lower than thesecond reference value (Yes at S105) or, in other words, when the outputvalue of the adjusting unit 130 is an output value 203 as illustrated inFIG. 4, the adjustment control unit 140 adjusts the setting of theadjusting unit 130, thereby adjusting (decreasing) the output value ofthe adjusting unit 130 to a predetermined voltage value equal to orhigher than the first reference value and lower than the secondreference value (S113). The process then ends. In this example, theadjustment control unit 140 adjusts the output value of the adjustingunit 130 to the first reference value by adjusting the setting of theadjusting unit 130, but this is not limited thereto.

In short, the adjustment control unit 140 performs the adjustmentoperation of adjusting the setting of the adjusting unit 130 so that thevoltage adjusted by the adjusting unit 130 falls within the range fromthe first reference value, inclusive, and the second reference value,exclusive. If the adjustment control unit 140 cannot adjust the settingof the adjusting unit 130 in the above-described manner, the adjustmentcontrol unit 140 determines that at least any one of the sending sensor112, the receiving sensor 114, and the adjusting unit 130 has failed.

A method for adjusting, by the adjusting control unit 140, the settingof the adjusting unit 130 is described below with reference to FIG. 5.FIG. 5 is a diagram illustrating an example of a circuit configurationof the receiving sensor 114 and the adjusting unit 130 according to theembodiment.

Referring to the example illustrated in FIG. 5, the receiving sensor 114includes a resistor 121. The resistance of the resistor 121 is minimizedat resonant frequency of the receiving sensor 114 with an impedance ofapproximately 300±100 ohms (Ω).

The adjusting unit 130 includes a step-down circuit including externalresistors R₁ to R_(n) and switches SW₁ to SW_(n). The adjusting unit 130can change a combined resistance value of the external resistors R₁ toR_(n) by switching on/off the switches SW₁ to SW_(n).

More specifically, the adjustment control unit 140 adjusts the settingof the adjusting unit 130 by switching on/off the switches SW₁ to SW_(n)so that a value of the voltage divided by the impedance of the resistor121 and the combined resistance value of the external resistors R₁ toR_(n) falls within the range from the first reference value, inclusive,and the second reference value, exclusive.

In the embodiment, it is assumed that the switches SW₁ to SW_(n) are alloff in the default setting. Decreasing the voltage by 30 dB can beperformed by switching on a predetermined number of the switches SW₁ toSW_(n).

Accordingly, in the embodiment, the adjustment control unit 140 switcheson the switches SW₁ to SW_(n) one by one so that the output value of theadjusting unit 130 achieves the first reference value and causes theadjusting unit 130 to maintain a state of the switches SW₁ to SW_(n) atwhich the output value of the adjusting unit 130 achieves the firstreference value. If the output value of the adjusting unit 130 should belower than the second reference value in a state where all the switchesSW₁ to SW_(n) are off or if the output value of the adjusting unit 130should be equal to or higher than the second reference value in a statewhere the predetermined number of the switches SW₁ to SW_(n) are on, theadjustment control unit 140 determines that at least any one of thesending sensor 112, the receiving sensor 114, and the adjusting unit 130has failed.

The determination as to whether the voltage value is equal to or higherthan the first reference value and equal to or lower than the secondreference value may be made using a comparator, an analog-to-digital(AD) converter, or the like. The determination may be made either by theadjusting unit 130 or by the adjustment control unit 140.

FIG. 5 illustrates an example in which the switches SW₁ to SW_(n) areanalog switches. However, when the sheet conveying device 100 conveyssheets of thick paper and thin paper, mechanical switches mayalternatively be employed as the switches SW₁ to SW_(n). A digitalpotentiometer or the like may preferably be employed when a certainlevel of accuracy in adjustment is required.

An operation for determining whether or not multi-feed has occurred(hereinafter, “multi-feed determination operation”) is described below.Note that the multi-feed determination operation is performed after theabove-described adjustment operation. For example, the multi-feeddetermination operation may be performed when a user performs a job,such as a print job, that uses a sheet.

The receiving sensor 114 receives an ultrasonic wave (an example of“first ultrasonic wave”) sent from the sending sensor 112 and passedthrough one sheet or, in a case of multi-feed, two or more sheets,converts the received ultrasonic wave into a voltage (an example of“first voltage”) representing the ultrasonic wave, and outputs thevoltage to the adjusting unit 130.

Thereafter, the adjusting unit 130 adjusts the voltage, into which theultrasonic wave is converted by the receiving sensor 114, into anadjusted voltage according to the setting adjusted by the adjustmentcontrol unit 140 and outputs the adjusted voltage to the amplificationunit 150. The output value of the adjusting unit 130 has thus undergoneadjustment that smoothes out device-to-device (device: the sheetconveying device 100) variation in the value of the ultrasonic wavecaused by the factor other than the factor of the sheet.

Thereafter, the amplification unit 150 amplifies the voltage adjusted bythe adjusting unit 130 by the preset multi-feed-determiningamplification factor and outputs the amplified voltage to thedetermining unit 160.

The preset multi-feed-determining amplification factor is anamplification factor for amplifying a voltage value obtained bysubtracting, from the value of the voltage adjusted by the adjustingunit 130, a voltage value corresponding to a maximum amount ofattenuation of the ultrasonic wave possibly caused by the factor of thesingle sheet from when the ultrasonic wave is sent from the sendingsensor 112 until when the ultrasonic wave is received by the receivingsensor 114 to an upper-limit output value of the amplification unit 150or higher.

However, the preset multi-feed-determining amplification factor issmaller than an amplification factor for amplifying a voltage valueobtained by subtracting, from the value of the voltage adjusted by theadjusting unit 130, a voltage value corresponding to a minimum amount ofattenuation of the ultrasonic wave possibly caused by the factor of twosheets when the ultrasonic wave is sent from the sending sensor 112until when the ultrasonic wave is received by the receiving sensor 114to the upper-limit output value of the amplification unit 150.

In the embodiment, the value of the voltage adjusted by the adjustingunit 130 is a voltage value obtained by subtracting, from the voltagevalue representing the ultrasonic wave sent from the sending sensor 112,a voltage value corresponding to a maximum amount of attenuation of theultrasonic wave possibly caused by the factor other than the factor ofthe sheet until when the ultrasonic wave is received by the receivingsensor 114.

Accordingly, in the embodiment, the preset multi-feed-determiningamplification factor is an amplification factor for amplifying avoltage, into which an ultrasonic wave sent from the sending sensor 112and received by the receiving sensor 114 after passing through one sheetin a condition where both the factor other than the factor of the sheetand the factor of the sheet maximize the amount of attenuation isconverted by the receiving sensor 114, to the upper-limit output valueof the amplification unit 150.

It should be noted that, in the embodiment, the presetmulti-feed-determining amplification factor is smaller than anamplification factor for amplifying a voltage, into which an ultrasonicwave sent from the sending sensor 112 and received by the receivingsensor 114 after passing through two sheets in a condition where boththe factor other than the factor of the sheet and the factor of thesheet minimize the amount of attenuation is converted by the receivingsensor 114, to the upper-limit output value of the amplification unit150.

Thereafter, the determining unit 160 determines whether or notmulti-feed of the sheets has occurred based on the voltage amplified bythe amplification unit 150.

More specifically, the determining unit 160 compares a value derivedfrom the voltage amplified by the amplification unit 150 with a valuederived from the upper-limit output value. The value derived from theamplified voltage may be either the amplified voltage itself or anintegral of the amplified voltage. The value derived from theupper-limit output value may be either the upper-limit output valueitself or an integral of the upper-limit output value.

The determining unit 160 determines that multi-feed has not occurred ifthe value derived from the voltage amplified by the amplification unit150 is equal to or higher than the value derived from the upper-limitoutput value. The reason therefor is described below. The presetmulti-feed-determining amplification factor of the embodiment is theamplification factor for amplifying the voltage representing theultrasonic wave sent from the sending sensor 114 to the upper-limitoutput value of the amplification unit 150 even in the condition whereboth the factor of the single-sheet and the factor other than the factorof the sheet maximize the amount of attenuation. Accordingly, whenmulti-feed has not occurred (i.e., the number of sheets is one), thevalue of the voltage amplified by the amplification unit 150 should beequal to or higher than the upper-limit output value without exception.

On the other hand, the determining unit 160 determines that multi-feedhas occurred if the value derived from the voltage amplified by theamplification unit 150 is lower than the value derived from theupper-limit output value. The reason therefor is described below. Thepreset multi-feed-determining amplification factor of the embodiment isthe amplification factor that is insufficient to amplify the voltagerepresenting the ultrasonic wave sent from the sending sensor 114 to theupper-limit output value of the amplification unit 150 even in thecondition where both the factor of the two sheets and the factor otherthan the factor of the sheet minimize the amount of attenuation.Accordingly, when multi-feed has occurred (i.e., the number of sheets istwo or more), the value of the voltage amplified by the amplificationunit 150 should be lower than the upper-limit output value withoutexception.

An operation for determining whether or not a failure has occurred(hereinafter, “failure determination operation”) is described below withreference to FIG. 6. FIG. 6 is a flowchart illustrating an example ofthe failure determination operation according to the embodiment. Notethat the failure determination operation is performed after theabove-described adjustment operation.

The receiving sensor 114 receives an ultrasonic wave (an example of“third ultrasonic wave”) sent from the sending sensor 112 and reachingthe receiving sensor 114 without passing through a sheet, converts thereceived ultrasonic wave into a voltage (an example of “third voltage”)representing the ultrasonic wave, and outputs the voltage to theadjusting unit 130.

Thereafter, the adjusting unit 130 adjusts the voltage, into which theultrasonic wave is converted by the receiving sensor 114, according tothe setting adjusted by the adjustment control unit 140 and outputs theadjusted voltage to the amplification unit 150 (S201). Morespecifically, at S201, the adjusting unit 130 adjusts (decreases) thevoltage, into which the ultrasonic wave is converted by the receivingsensor 114, to a voltage value obtained by subtracting, from the valueof the voltage adjusted according to the setting adjusted by theadjusting control unit 140 through the adjustment operation, a voltagevalue corresponding to a maximum amount of attenuation of the ultrasonicwave possibly caused by the factor of the single sheet from when theultrasonic wave is sent from the sending sensor 112 until when theultrasonic wave is received by the receiving sensor 114, and outputs thethus-adjusted voltage value to the amplification unit 150. It is assumedthat the setting for adjusting the voltage, into which the ultrasonicwave is converted by the receiving sensor 114, to such a voltage valueas that described above have been configured in advance by theadjustment control unit 140.

The operation described above causes the adjusting unit 130 to output avalue that is to be output in a condition where the factor of the singlesheet maximizes the amount of attenuation of the ultrasonic wavereceived by the receiving sensor 114. As a result, because thedetermining unit 160 can make a pseudo determination that multi-feed hasoccurred, the determining unit 160 can make the failure determination.

Thereafter, the amplification unit 150 amplifies the voltage adjusted bythe adjusting unit 130 by the preset multi-feed-determiningamplification factor and outputs the amplified voltage to thedetermining unit 160.

Thereafter, the determining unit 160 compares a value derived from thevoltage amplified by the amplification unit 150 with a value derivedfrom the upper-limit output value. The determining unit 160 determinesthat multi-feed has not occurred if the value derived from the voltageamplified by the amplification unit 150 is equal to or higher than thevalue derived from the upper-limit output value, but determines thatmulti-feed has occurred if the value is lower than the value derivedfrom the upper-limit output value (S203).

As described above, the adjusting unit 130 outputs the value that is tobe output in the condition where the factor of the single sheetmaximizes the amount of attenuation of the ultrasonic wave received bythe receiving sensor 114. Accordingly, the result of determination madeby the determining unit 160 should be that multi-feed has not occurredwithout exception. If the result of determination made by thedetermining unit 160 should be that multi-feed has occurred (No atS203), the determining unit 160 determines that at least any one of theadjusting unit 130, the amplification unit 150, and the determining unit160 has failed (S205), and sends a notification of the failure to thecontrol unit (not shown) or the like so that the failure is displayed onthe display unit (not shown) or the like.

Meanwhile, conditions of the sending sensor 112 and the receiving sensor114 remain the same as those in the adjustment operation. Becausefailure determination of the sending sensor 112 and the receiving sensor114 has been made at the adjustment operation, repeated failuredetermination is omitted from S203.

On the other hand, if the result of determination made by thedetermining unit 160 is that multi-feed has not occurred (Yes at S203),the receiving sensor 114 receives an ultrasonic wave (an example of“fourth ultrasonic wave”) sent from the sending sensor 112 and reachingthe receiving sensor 114 without passing through a sheet, converts thereceived ultrasonic wave into a voltage (an example of “fourth voltage”)representing the ultrasonic wave, and outputs the voltage to theadjusting unit 130.

Thereafter, the adjusting unit 130 adjusts the voltage, into which theultrasonic wave is converted by the receiving sensor 114, according tothe setting adjusted by the adjustment control unit 140 and outputs theadjusted voltage to the amplification unit 150 (S207). Morespecifically, at S207, the adjusting unit 130 adjusts (decreases) thevoltage, into which the ultrasonic wave is converted by the receivingsensor 114, to a voltage value obtained by subtracting, from the valueof the voltage adjusted according to the setting adjusted by theadjusting control unit 140 through the adjustment operation, a voltagevalue corresponding to a minimum amount of attenuation of the ultrasonicwave possibly caused by the factor of the two sheets from when theultrasonic wave is sent from the sending sensor 112 until when theultrasonic wave is received by the receiving sensor 114, and outputs thethus-adjusted voltage value to the amplification unit 150. It is assumedthat the setting for adjusting the voltage, into which the ultrasonicwave is converted by the receiving sensor 114, to such a voltage valueas that described above has been configured by the adjustment controlunit 140 after S203.

The adjustment described above causes the adjusting unit 130 to output avalue that is to be output in a condition where the factor of the twosheets minimizes the amount of attenuation of the ultrasonic wavereceived by the receiving sensor 114. Accordingly, because thedetermining unit 160 can make a pseudo determination that multi-feed hasoccurred, the determining unit 160 can make the failure determination.

Thereafter, the amplification unit 150 amplifies the voltage adjusted bythe adjusting unit 130 by the preset multi-feed-determiningamplification factor and outputs the amplified voltage to thedetermining unit 160.

Thereafter, the determining unit 160 compares a value derived from thevoltage amplified by the amplification unit 150 with a value derivedfrom the upper-limit output value. The determining unit 160 determinesthat multi-feed has not occurred if the value derived from the voltageamplified by the amplification unit 150 is equal to or higher than thevalue derived from the upper-limit output value, but determines thatmulti-feed has occurred if the value is lower than the value derivedfrom the upper-limit output value (S209).

As described above, the adjusting unit 130 outputs the value that is tobe output in the condition where the factor of the two sheets minimizesthe amount of attenuation of the ultrasonic wave received by thereceiving sensor 114. Accordingly, the result of determination made bythe determining unit 160 should be that multi-feed has occurred withoutexception. If the result of determination made by the determining unit160 should be that multi-feed has not occurred (No at S209), thedetermining unit 160 determines that at least any one of the adjustingunit 130, the amplification unit 150, and the determining unit 160 hasfailed (S211), and sends a notification of the failure to the controlunit (not shown) or the like so that the failure is displayed on thedisplay unit (not shown) or the like. Examples of failure of theamplification unit 150 include anomalous origination from an operationalamplifier.

Meanwhile, conditions of the sending sensor 112 and the receiving sensor114 remain the same as those in the adjustment operation. Becausefailure determination of the sending sensor 112 and the receiving sensor114 has been made at the adjustment operation, repeated failuredetermination is omitted from S209.

On the other hand, if the result of determination made by thedetermining unit 160 is that multi-feed has occurred (Yes at S209), thedetermining unit 160 determines that the adjusting unit 130, theamplification unit 150, and the determining unit 160 are normal (S213).

Thereafter, the adjustment control unit 140 brings the setting of theadjusting unit 130 back to the setting adjusted in the adjustmentoperation.

As described above, according to the embodiment, because the adjustingunit 130 adjusts variation in the ultrasonic wave caused by the factorother than the factor of the sheet, the amplification unit 150 can use afixed amplification factor. Accordingly, according to the embodiment, anundesirable situation that characteristics of a noise filter in theamplification unit 150 are changed or undesirable oscillation of theoperational amplifier that would otherwise occur in multi-feeddetermination can be prevented. As a result, accuracy in multi-feeddetermination can be further increased.

According to the embodiment, variation in the ultrasonic wave caused bythe factor other than the factor of the sheet is adjusted using theadjusting unit 130 by adjusting the setting of the adjusting unit 130.Accordingly, even if the sending sensor 112, the receiving sensor 114,or the like is replaced after shipment of the sheet conveying device 100and positional relationship has changed from before the replacement,variation in ultrasonic wave caused by the factor other than the factorof the sheet can be reduced by adjusting the setting of the adjustingunit 130.

According to the embodiment, the setting of the adjusting unit 130 isadjusted in a state where no sheet is conveyed by the sheet conveyingdevice 100, in contrast to the technique disclosed in Japanese Laid-openPatent Application No. 2006-312527 in which the amplification factor isadjusted during sheet conveyance. Accordingly, enhancing productivity ofprinted matter and the like can also be achieved.

According to the embodiment, whether or not a failure has occurred inelements upstream of the adjusting unit 130 can be determined byadjusting the setting of the adjusting unit 130. Accordingly,considerable reduction in time required to locate a position where afailure has occurred can be achieved.

According to the embodiment, whether or not a failure has occurred inelements downstream of the adjusting unit 130 can be determined byperforming the failure determination operation of making a pseudodetermination that multi-feed has occurred after the adjustmentoperation that adjusts the setting of the adjusting unit 130.Accordingly, considerable reduction in time required to locate aposition where a failure has occurred can be achieved.

Modifications

The embodiment may be modified so that the adjustment operation isperformed in the following manner. The adjustment control unit 140adjusts the voltage adjusted by the adjusting unit 130 simply to avoltage within the range from the first reference value, inclusive, tothe second reference value, exclusive rather than adjusting the outputvoltage of the adjusting unit 130 to the predetermined voltage valuewithin the range.

In this case, the preset multi-feed-determining amplification factor ispreferably an amplification factor for amplifying a voltage, into whichan ultrasonic wave sent from the sending sensor 112 and received by thereceiving sensor 114 after passing through one sheet in a conditionwhere both the factor other than the factor of the sheet and the factorof the sheet maximize the amount of attenuation is converted by thereceiving sensor 114, to the upper-limit output value of theamplification unit 150 and is smaller than an amplification factor foramplifying a voltage, into which an ultrasonic wave sent from thesending sensor 112 and received by the receiving sensor 114 afterpassing through two sheets in a condition where both the factor otherthan the factor of the sheet and the factor of the sheet minimize theamount of attenuation is converted by the receiving sensor 114, to theupper-limit output value of the amplification unit 150.

The embodiment may be modified to use the first reference value and thesecond reference value described below which differ from those of theembodiment. The second reference value of the modification is a voltagevalue obtained by subtracting, from the voltage value representing theultrasonic wave sent from the sending sensor 112, a voltage valuecorresponding to a minimum amount of attenuation of the ultrasonic wavepossibly caused by the factor other than the factor of the sheet in theperiod until when the ultrasonic wave is received by the receivingsensor 114. The first reference value of the modification is a voltagevalue within a range between the second reference value and a voltagevalue obtained by subtracting, from the voltage value representing theultrasonic wave sent from the sending sensor 112, a voltage valuecorresponding to a maximum amount of attenuation of the ultrasonic wavepossibly caused by the factor other than the factor of the sheet untilwhen the ultrasonic wave is received by the receiving sensor 114. Inthis case, the adjustment control unit 140 may preferably adjust thesetting of the adjusting unit 130 by increasing the voltage rather thandecreasing the voltage by setting the first reference value aftersetting the second reference value in contrast to the embodiment inwhich the first reference value is set before the second referencevalue.

Hardware Configuration

FIG. 7 is a block diagram illustrating an example of a hardwareconfiguration of an image forming apparatus 900 to which the sheetconveying device 100 according to the embodiment is applied. Asillustrated in FIG. 7, the image forming apparatus 900 of the embodimentincludes a controller 910 and an engine unit (Engine) 960 that areconnected to each other via a PCI (peripheral component interconnect)bus. The controller 910 controls the entire image forming apparatus 900,image formation, communication, and inputs entered using anoperating-and-display unit 920. The engine unit 960 is a printer engineor the like connectable to the PCI bus. The engine unit 960 may be, forexample, a monochrome plotter, a one-drum color plotter, a four-drumcolor plotter, or a scanner or facsimile unit. The engine unit 960includes, in addition to what is referred generally to as an engine partsuch as the plotter, a part that performs image processing includingerror diffusion, gamma conversion, and/or the like.

The controller 910 includes a CPU (central processing unit) 911, an NB(north bridge) 913, a system memory (MEM-P) 912, an SB (south bridge)914, a local memory (MEM-C) 917, an ASIC (application specificintegrated circuit) 916, an HDD (hard disk drive) 918, and an AGP(accelerated graphics port) bus 915. The AGP bus 915 connects betweenthe NB 913 and the ASIC 916. The MEM-P 912 includes a ROM (read onlymemory) 912 a and a RAM (random access memory) 912 b.

The CPU 911 provides overall control of the image forming apparatus 900and includes a chipset made up of the NB 913, the MEM-P 912, and the SB914. The CPU 911 is connected to other equipment via the chipset.

The NB 913 that bridges the CPU 911 to the MEM-P 912, the SB 914, andthe AGP bus 915 includes a PCI master, an AGP target, and a memorycontroller that controls writing and reading to and from the MEM-P 912.

The MEM-P 912 is a system memory for use as a memory for storing programinstructions and data, a memory into which program instructions and dataare to be loaded, a memory for printer buffer, and the like, andincludes the ROM 912 a and the RAM 912 b. The ROM 912 a is a read onlymemory for use as the memory for storing program instructions and data.The RAM 912 b is a writable and readable memory for use as the memoryinto which program instructions and data are to be loaded, the memoryfor printer buffer, and the like.

The SB 914 bridges the NB 913 to a PCI device and a peripheral device.This SB 914 is connected to the NB 913 via the PCI bus. A network I/F(interface) and the like can also be connected to the PCI bus.

The ASIC 916 is an IC (integrated circuit) for image processing andincludes hardware elements for the image processing. The ASIC 916 servesas a bridge that connects the AGP bus 915, the PCI bus, the HDD 918, andthe MEM-C 917 to each other. This ASIC 916 includes a PCI target and anAGP master, an ARB (arbiter) serving as the core of the ASIC 916, amemory controller that controls the MEM-C 917, a plurality of DMACs(direct memory access controllers) that perform image data rotation andthe like by hardware logic or the like, and a PCI unit that transfersdata to and from the engine unit 960 via the PCI bus. An FCU (facsimilecontrol unit) 930, a USB (universal serial bus) 940, and an IEEE 1394(the Institute of Electrical and Electronics Engineers 1394) I/F 950 areconnected to the ASIC 916 via the PCI bus. The operating-and-displayunit 920 is directly connected to the ASIC 916.

The MEM-C 917 is a local memory for use as an image buffer for thecopier function and a code buffer. The HDD 918 is storage for storingimage data, program instructions, font data, and forms.

The AGP bus 915 is a bus interface for a graphics accelerator cardintroduced to speed up graphics operations. The AGP bus 915 allowsdirect access to the MEM-P 912 with a high throughput, thereby speedingup operations related to the graphic accelerator card.

According to an embodiment, accuracy in multi-feed determination can beincreased.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

What is claimed is:
 1. A sheet conveying device comprising: a sendingunit configured to send an ultrasonic wave; a receiving unit positionedto face the sending unit across a conveyance path, along which a sheetis conveyed, and configured to receive a first ultrasonic wave, thefirst ultrasonic wave being an ultrasonic wave sent from the sendingunit and passed through the sheet, and output a first voltagecorresponding to the first ultrasonic wave; an adjusting unit configuredto adjust the first voltage into an adjusted first voltage according toa setting; an amplification unit configured to amplify the adjustedfirst voltage by a preset amplification factor for multi-feeddetermination into an amplified first voltage; and a determining unitconfigured to determine whether or not multi-feed of the sheet hasoccurred based on the amplified first voltage.
 2. The sheet conveyingdevice according to claim 1, further comprising an adjustment controlunit, wherein the receiving unit receives a second ultrasonic wave, thesecond ultrasonic wave being an ultrasonic wave sent from the sendingunit and reaching the receiving unit without passing through the sheet,and outputs a second voltage corresponding to the second ultrasonicwave, and the adjustment control unit adjusts the setting such that anadjusted second voltage, into which the adjusting unit adjusting thesecond voltage, falls within a range between a first reference value,inclusive, and a second reference value, exclusive.
 3. The sheetconveying device according to claim 2, wherein if the adjustment controlunit is incapable of adjusting the setting such that the adjusted secondvoltage falls within the range between the first reference value,inclusive, and the second reference value, exclusive, the adjustmentcontrol unit determines that any of the sending unit, the receivingunit, and the adjusting unit has failed.
 4. The sheet conveying deviceaccording to claim 2, wherein the first reference value is a voltagevalue obtained by subtracting, from the voltage value corresponding tothe ultrasonic wave sent from the sending unit, a voltage valuecorresponding to a maximum amount of attenuation of the ultrasonic wavepossibly caused by a factor other than a factor of the sheet until whenthe ultrasonic wave is received by the receiving unit, and the secondreference value is a voltage value within a range between the firstreference value and a voltage value obtained by subtracting, from thevoltage value corresponding to the ultrasonic wave sent from the sendingunit, a voltage value corresponding to a minimum amount of attenuationof the ultrasonic wave possibly caused by the factor other than thefactor of the sheet until when the ultrasonic wave is received by thereceiving unit.
 5. The sheet conveying device according to claim 2,wherein the second reference value is a voltage value obtained bysubtracting, from the voltage value corresponding to the ultrasonic wavesent from the sending unit, a voltage value corresponding to a minimumamount of attenuation of the ultrasonic wave possibly caused by thefactor other than the factor of the sheet until when the ultrasonic waveis received by the receiving unit, and the first reference value is avoltage value within a range between the second reference value and avoltage value obtained by subtracting, from the voltage valuecorresponding to the ultrasonic wave sent from the sending unit, avoltage value corresponding to a maximum amount of attenuation of theultrasonic wave possibly caused by the factor other than the factor ofthe sheet until when the ultrasonic wave is received by the receivingunit.
 6. The sheet conveying device according to claim 1, wherein thepreset amplification factor for multi-feed determination is anamplification factor by which at least a voltage value obtained bysubtracting, from the value of the voltage adjusted according to thesetting, a voltage value corresponding to a maximum amount ofattenuation of the ultrasonic wave possibly caused by a factor of asingle sheet from when the ultrasonic wave is sent from the sending unituntil when the ultrasonic wave is received by the receiving unit isamplified to an upper-limit output value of the amplification unit, theamplification factor being smaller than an amplification factor by whicha voltage value obtained by subtracting, from the value of the voltageadjusted according to the setting, a voltage value corresponding to aminimum amount of attenuation of the ultrasonic wave possibly caused bya factor of two sheets from when the ultrasonic wave is sent from thesending unit until when the ultrasonic wave is received by the receivingunit is amplified to the upper-limit output value of the amplificationunit, and the determining unit compares a value derived from theamplified first voltage with a value derived from the upper-limit outputvalue, and determines that multi-feed has not occurred if the valuederived from the amplified first voltage is equal to or higher than thevalue derived from the upper-limit output value but determines thatmulti-feed has occurred if the value derived from the amplified firstvoltage is lower than the value derived from the upper-limit outputvalue.
 7. The sheet conveying device according to claim 6, wherein thereceiving unit receives a fourth ultrasonic wave, the fourth ultrasonicwave being an ultrasonic wave sent from the sending unit and reachingthe receiving unit without passing through the sheet, and outputs afourth voltage corresponding to the fourth ultrasonic wave, theadjusting unit adjusts the fourth voltage to an adjusted fourth voltageby subtracting, from a voltage value obtained by adjusting the fourthvoltage according to the setting, the voltage value corresponding to themaximum amount of attenuation of the ultrasonic wave possibly caused bythe factor of the single sheet from when the ultrasonic wave is sentfrom the sending unit until when the ultrasonic wave is received by thereceiving unit, the amplification unit amplifies the adjusted fourthvoltage by the preset amplification factor for multi-feed determinationinto an amplified fourth voltage, and the determining unit compares avalue derived from the amplified fourth voltage with the value derivedfrom the upper-limit output value, and determines that at least any ofthe adjusting unit, the amplification unit, and the determining unit hasfailed if the value derived from the amplified fourth voltage is lowerthan the value derived from the upper-limit output value.
 8. The sheetconveying device according to claim 6, wherein the receiving unitreceives a third ultrasonic wave, the third ultrasonic wave being anultrasonic wave sent from the sending unit and reaching the receivingunit without passing through the sheet, and outputs a third voltagecorresponding to the third ultrasonic wave, the adjusting unit adjuststhe third voltage to an adjusted third voltage by subtracting, from avoltage value obtained by adjusting the third voltage according to thesetting, the voltage value corresponding to the minimum amount ofattenuation of the ultrasonic wave possibly caused by the factor of thetwo sheets from when the ultrasonic wave is sent from the sending unituntil when the ultrasonic wave is received by the receiving unit, theamplification unit amplifies the adjusted third voltage by the presetamplification factor for multi-feed determination into an amplifiedthird voltage, and the determining unit compares a value derived fromthe amplified third voltage with the value derived from the upper-limitoutput value, and determines that at least any of the adjusting unit,the amplification unit, and the determining unit has failed if the valuederived from the amplified third voltage is equal to or higher than thevalue derived from the upper-limit output value.
 9. An image formingapparatus comprising the sheet conveying device according to claim 1.10. A method of determining whether or not multi-feed has occurred, themethod comprising: sending an ultrasonic wave; receiving includingreceiving the ultrasonic wave passed through a sheet conveyed along aconveyance path and outputting a voltage corresponding to the ultrasonicwave; adjusting the voltage into an adjusted voltage according to asetting; amplifying the adjusted voltage by a preset amplificationfactor for multi-feed determination into an amplified voltage; anddetermining whether or not multi-feed of the sheet has occurred based onthe amplified voltage.